a) Field of the Invention
This invention relates to (co)polymer particles having a function to be substantially redispersible in water of pH 5 or higher and also to a process for the production of the (co)polymer particles.
b) Description of the Related Art
An aqueous emulsion available by emulsion polymerization generally contains as much as 30 to 90 wt. % of water as a dispersion medium. This means that upon its piping or shipping, a great deal of water has to be transported, thereby causing a problem from the standpoint of both energy and cost.
On the other hand, a redispersible polymer is, in contrast to general aqueous emulsions, in the form of a solid or paste which is either completely or substantially free of water, and permits easy piping, shipping and storage. As another characteristic feature, a redispersible polymer can be reconstituted into an emulsified form similar to an ordinary aqueous emulsion by dissolving it in water when needed.
A redispersible polymer or a powder thereof can be premixed with another powder such as cement, gypsum or a pigment in accordance with a desired formula and can hence be provided as a one-pack product.
One-pack products with a redispersible polymer or a powder thereof premixed therein are widely used in the field of cement modifiers.
Such one-pack products with a redispersible polymer or a powder thereof premixed therein are in the form of compact light-weight powders during their piping, shipping and storage but upon use, mixing of such powders with water at construction sites makes it possible to prepare desired concretes in a single-step operation for immediate use.
Upon mixing a polymer, irksome procedures such as measuring operations can be significantly omitted so that the efficiency of work becomes extremely good. This is substantially meritorious.
Gallon cans or drum cans are needed in the case of a conventional aqueous emulsion. They are however no longer needed in the case of a redispersible polymer of a powder thereof. This is advantageous in that packaging cost can be reduced at the time of shipping and packaging materials, such as gallon cans and drum cans, to be disposed can be substantially reduced in quantity.
When provided as a premixed one-pack product, the quality control of concrete at the time of construction is made easier and the reliability of the construction is improved further, because its components have been precisely measured beforehand in accordance with a desired formula.
Compared with conventional aqueous emulsions, the redispersible polymer or its powder according to the present invention is therefore advantageous at least for the following reasons:
(1) It is possible to reduce the cost and energy required for piping, shipping or storage. PA1 (2) The packaging cost can be reduced as large liquid containers are no longer needed. PA1 (3) Industrial waste can be reduced since large liquid container are no longer needed. PA1 (4) When provided in the form of a premixed one-pack product, measuring operation at a construction site is practically obviated so that substantial labor savings can be achieved. PA1 (5) When provided in the form of a premixed one-pack product, mixing of the powder with water makes it possible to prepare desired concrete in a single step, thereby attaining substantial labor savings. PA1 (6) When provided in the form of a premixed one-pack product, the quality control of concrete can be facilitated at the time of construction because each component has been precisely measured in accordance with a desired formula. PA1 (1) Their redispersibility is not sufficient, because particles thermally cohere with one another under heat in conventional spray drying. PA1 (2) Conventional spray drying requires a large facility and consumes a great deal of energy, and therefore is disadvantageous in cost. PA1 (1) a function as a stabilizer for stably performing the emulsion polymerization; and PA1 (2) a function as a powdering agent for obtaining an aggregate-free powder. PA1 (1) Powdering of a polymer: this is a theme to cause precipitation of (co)polymer particles in a polymer emulsion without aggregation. PA1 (2) Redispersion of a powdered polymer: this is a theme to provide the (co)polymer particles, which has been converted into powder as described above under (1), with a function to be substantially redispersible in water of pH 5 or higher. PA1 said particles have a core/shell structure with at least a part of a surface of each core being covered with an associated shell; PA1 said core is made of a (co)polymer (.alpha.2) composed of a recurring unit and 0 wt. % or more but less than 40 wt. % of at least one recurring unit selected from the group consisting of recurring units having pendant groups represented by the following formula (1) and the group consisting of recurring units having pendant groups represented by the following formula (2): ##STR1## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms; PA1 said shell is made of a (co)polymer (.alpha.1) composed of a recurring unit and 20 wt. % or more but not greater than 100 wt. % of at least one recurring unit selected from the group consisting of said recurring units having said pendant groups represented by the formula (1) and the group consisting of said recurring units having said pendant groups represented by the formula (2); PA1 based on the total weight of (.alpha.1) and (.alpha.2), (.alpha.1) ranges from 15 to 85 wt. % while (.alpha.2) ranges from 85 to 15 wt. %; and PA1 said at least one recurring unit having said pendant group represented by the formula (1) and/or (2) in (.alpha.1) is contained at a higher content than said at least one recurring unit in (.alpha.2). PA1 said (co)polymer is a mixture of particles (A) and a protective colloid; PA1 said particles (A) are made of a (co)polymer (.alpha.2) composed of a recurring unit and 0 wt. % or more but less than 40 wt. % of at least one recurring unit selected from the group consisting of recurring units having pendant groups represented by the following formula (1) and the group consisting of recurring units having pendant groups represented by the following formula (2): ##STR2## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms; PA1 said protective colloid is made of a (co)polymer (.alpha.1) composed of a recurring unit and 20 wt. % or more but not greater than 100 wt. % of at least one recurring unit selected from the group consisting of said recurring units having said pendant groups represented by the formula (1) and the group consisting of said recurring units having said pendant groups represented by the formula (2); PA1 based on the total weight of (.alpha.1) and (.alpha.2), (.alpha.1) ranges from 15 to 85 wt. % while (.alpha.2) ranges from 85 to 15 wt. %; and PA1 said at least one recurring unit having said pendant group represented by the formula (1) and/or (2) in (.alpha.1) is contained at a higher content than said at least one recurring unit in (.alpha.2). PA1 a protective colloid (.alpha.1) obtained by radical (co)polymerization of an ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one monomer selected from the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (1) and the group consisting of ethylenically unsaturated monomers having pendant groups represented by the formula (2): ##STR5## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms, and PA1 an ethylenically unsaturated monomer for forming a copolymer (a2), said ethylenically unsaturated monomer comprising 0 wt. % or more but less than 40 wt. % of at least one monomer selected from the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (1) and the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (2), PA1 adding a mineral acid and/or an organic acid to said aqueous emulsion, which has been prepared in step 1, to adjust the pH of said aqueous emulsion to 4 or lower, whereby said (co)polymer particles (A) are caused to flocculate and a flocculate (A') of said (co)polymer is formed. PA1 emulsion (co)polymerizing, into a (co)polymer (a2), an ethylenically unsaturated monomer comprising 0 wt. % or more but less than 40 wt. % of at least one monomer selected from the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (1) and the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (2): ##STR6## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms, whereby an aqueous emulsion formed of a dispersed phase of (co)polymer core particles (A.degree.) and a continuous phase of water is prepared; PA1 said (co)polymer core particles (A') in said aqueous emulsion prepared in step 1, and an ethylenically unsaturated monomer for forming a copolymer (a1), said ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one monomer selected from the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (1) and the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (2), PA1 adding a mineral acid and/or an organic acid to said aqueous emulsion, which has been prepared in step 2, to adjust the pH of said aqueous emulsion to 4 or lower, whereby said core/shell (co)polymer particles (A) are caused to flocculate and a flocculate (A') of said (co)polymers is formed. PA1 emulsion (co polymerizing, into a (co)polymer (a2), an ethylenically unsaturated monomer comprising 0 wt. % or more but less than 40 wt. % of at least one monomer selected from the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (1) and the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (2): ##STR7## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms, whereby an aqueous emulsion formed of a dispersed phase of (co)polymer core particles (A.degree.) and a continuous phase of water is prepared; PA1 conducting radical (co)polymerization of an ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one monomer selected from the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (1) and the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (2), whereby a protective colloid (a1) is prepared; PA1 mixing said aqueous emulsion prepared in step 1 with said protective colloid prepared in step 2 so that based on the total weight of (a1) and (a2), (a1) ranging from 15 to 85 wt. % while (a2) ranging from 85 to 15 wt. % and said at least one monomer having said pendant group represented by the formula (1) and/or (2) in (a1) is contained at a higher content than said at least one monomer in (a2); and PA1 adding a mineral acid and/or an organic acid to a mixture of said aqueous emulsion and said protective colloid, which has been obtained in step 3, to adjust the pH of said mixture to 4 or lower, whereby said (co)polymer particles (A) and said protective colloid are caused to flocculate and a flocculate (A') of said (co)polymers is formed. PA1 an ethylenically unsaturated monomer for forming a copolymer (a2), said ethylenically unsaturated monomer comprising 0 wt. % or more but less than 40 wt. % of at least one monomer selected from the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (1) and the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (2), PA1 adding a metal salt to said aqueous emulsion, which has been prepared in step 1, to salt out said (co)polymer particles (A), whereby a flocculate (A') of said (co)polymer is formed. PA1 emulsion (co)polymerizing, into a (co)polymer (a2) , an ethylenically unsaturated monomer comprising 0 wt. % or more but less than 40 wt. % of at least one monomer selected from the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (1) and the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (2): ##STR9## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms, whereby an aqueous emulsion formed of a dispersed phase of (co)polymer core particles (A.degree.) and a continuous phase of water is prepared; PA1 said (co)polymer core particles (A.degree.) in said aqueous emulsion prepared in step 1, and PA1 an ethylenically unsaturated monomer for forming a copolymer (a1), said ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one monomer selected from the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (1) and the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (2), PA1 adding a metal salt to said aqueous emulsion, which has been prepared in step 2, to salt out said core/shell (co)polymer particles (A), whereby a flocculate (A') of said (co)polymer is formed. PA1 emulsion (co)polymerizing, into a (co)polymer (a2), an ethylenically unsaturated monomer comprising 0 wt. % or more but less than 40 wt. % of at least one monomer selected from the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (1) and the group consisting of ethylenically unsaturated monomers having pendant groups represented by the following formula (2): ##STR10## wherein in the formula (1), R.sup.1 and R.sup.2 are either the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, or an OH-containing alkyl group having 1-12 carbon atoms and in the formula (2), R.sup.3 represents an alkylene group having 1-30 carbon atoms or R.sup.3, together with the hydroxyl group bonded thereto, represents --(R.sup.22 --O).sub.n --H in which n stands for an integer of 2 to 33 and R.sup.22 s may be the same or different and individually represents an alkylene group having 2-5 carbon atoms, whereby an aqueous emulsion formed of a dispersed phase of (co)polymer core particles (A.degree.) and a continuous phase of water is prepared; PA1 conducting radical (co)polymerization of an ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one monomer selected from the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (1) and the group consisting of said ethylenically unsaturated monomers having said pendant groups represented by the formula (2); PA1 mixing said aqueous emulsion prepared in step 1 with said protective colloid prepared in step 2 so that based on the total weight of (a1) and (a2), (a1) ranges from 15 to 85 wt. % while (a2) ranges from 85 to 15 wt. % and said at least one monomer having said pendant group represented by the formula (1) and/or (2) in (a1) is contained at a higher content than said at least one monomer in (a2); and PA1 adding a metal salt to a mixture of said aqueous emulsion and said protective colloid, which has been obtained in step 3, to salt out said (co)polymer particles (A) and said protective colloid, whereby a flocculate (A') of said (co)polymer is formed. PA1 said (co)polymer is in the form of particles having a shell/core structure with at least a part of a surface of each core being covered with an associated shell; PA1 said core is made of a water-insoluble (co)polymer; and PA1 said shell is made of a (co)polymer water-soluble at pH 5 or higher. PA1 said (co)polymer is in the form of particles having a shell/core structure with at least a part of a surface of each core being covered with an associated shell; PA1 said core is made of a water-insoluble (co)polymer; PA1 said shell is made of a (co)polymer water-soluble at pH 5 or higher; and PA1 said shells account for at least 15 wt. % of the total weight of said cores and said shells. PA1 said particles have a shell/core structure with at least a part of a surface of each core being covered with an associated shell; PA1 said cores have a glass transition point in a range of from -40 to +30.degree. C.; and PA1 said shells have a glass transition point at least 10.degree. C. higher than said glass transition point of said cores, account for at least 15 wt. % of the total weight of said particles, and have a function to flocculate at pH 4 or lower. PA1 (1) a structure generally called the "core/shell" type, in which the surface of the (co)polymer particle of the ethylenically unsaturated monomer (a2), said particle being contained in each particle, is fully covered with the protective colloid (a1); PA1 (2) a structure in which the protective colloid (a1) is deposited on a part of the (co)polymer particle of the ethylenically unsaturated monomer (a2), said particle being contained in each particle, and the surface of the (co)polymer particle is not fully covered with the protective colloid; and PA1 (3) a so-called salami structure in which the protective colloid (a1) is contained in each (co)polymer particle of the ethylenically unsaturated monomer (a2). PA1 (1) A (co)polymer formed of particles and having a function to be substantially redispersible in water of pH 5 or higher, wherein: PA1 said shell is made of a (co)polymer (.alpha.1) composed of a recurring unit and 20 wt. % or more but not greater than 100 wt. % of at least one recurring unit selected from the group consisting of said recurring units having said pendant groups represented by the formula (1) and the group consisting of said recurring units having said pendant groups represented by the formula (2); PA1 based on the total weight of (.alpha.1) and (.alpha.2), (.alpha.1) ranges from 15 to 85 wt. % while (.alpha.2) ranges from 85 to 15 wt. %; and PA1 said at least one recurring unit having said pendant group represented by the formula (1) and/or (2) in (.alpha.1) is contained at a higher content than said at least one recurring unit in (.alpha.2). PA1 (2) A (co)polymer having a function to be substantially redispersible in water of pH 5 or higher, wherein: PA1 (3) A (co)polymer according to claim 1 or 2, wherein of said recurring units making up each of (.alpha.1) and (.alpha.2), the recurring unit other than said at least one recurring unit having said pendant group represented by the formula (1) and/or (2) is composed of at least one of the following structural units (v) to (z): ##STR14## wherein R.sup.11 represents a hydrogen atom or a methyl group, R.sup.12 represents a hydrogen atom or an alkyl group having 1-12 carbon atoms, R.sup.13 represents a hydrogen atom, an alkyl group having 1-20 carbon atoms, an alkenyl group having 1-20 carbon atoms or a phenyl group, R.sup.14 s are the same or different and individually represent a hydrogen atom, an alkyl group having 1-12 carbon atoms, a sulfonic group or a metal sulfonate group, and R.sup.15 represents a divalent hydrocarbon group having 1-6 carbon atoms. PA1 (4) A (co)polymer substantially redispersible at pH 5 or higher, wherein: PA1 (5) A (co)polymer substantially redispersible at pH 5 or higher, wherein: PA1 (6) Particles substantially free of intraparticular blocking property, wherein: PA1 (7) A (co)polymer formed of particles and having a function to be substantially redispersible in water of pH 5 or higher, wherein: PA1 said shell is made of a (co)polymer (.alpha.1) of an ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one ethylenically unsaturated monomer selected from the group consisting of said recurring units having said pendant groups represented by the formula (1) and the group consisting of said recurring units having said pendant groups represented by the formula (2); PA1 based on the total weight of (.alpha.1) and (.alpha.2), (.alpha.1) ranges from 15 to 85 wt. % while (.alpha.2) ranges from 85 to 15 wt. %; and PA1 said at least one ethylenically unsaturated monomer having said pendant group represented by the formula (.alpha.1) is contained at a higher content than said at least one ethylenically unsaturated monomer in (.alpha.2). PA1 (8) A (co)polymer having a function to be substantially redispersible in water of pH 5 or higher, wherein: PA1 said protective colloid is made of a (co)polymer (.alpha.1) of an ethylenically unsaturated monomer comprising 20 wt. % or more but not greater than 100 wt. % of at least one ethylenically unsaturated monomer selected from the group consisting of said recurring units having said pendant groups represented by the formula (1) and the group consisting of said recurring units having said pendant groups represented by the formula (2); PA1 based on the total weight of (.alpha.1) and (.alpha.2), (.alpha.1) ranges from 15 to 85 wt. % while (.alpha.2) ranges from 85 to 15 wt. %; and PA1 said at least one recurring unit having said pendant group represented by the formula (1) and/or (2) in (.alpha.1) is contained at a higher content than said at least one recurring unit in (.alpha.2). PA1 (1) van der Waals attraction (intermolecular attraction), PA1 (2) electrostatic repulsion, and PA1 (3) steric repulsion at particle surfaces. PA1 (1) Acrylates of alkyl groups having 1-12 carbon atoms, such as methyl, ethyl, isopropyl, n-butyl, isobutyl, n-amyl, isoamyl, n-hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, cyclohexyl, phenyl, and benzyl acrylates. PA1 (2) Methacrylates of alkyl groups having 1-12 carbon atoms, such as methyl, ethyl, isopropyl, n-butyl, isobutyl, n-amyl, isoamyl, n-hexyl, 2-ethyl-hexyl, octyl, decyl, dodecyl, octadecyl, cyclohexyl, phenyl, and benzyl methacrylates. PA1 (3) Others such as glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, isopropenyl-.alpha.,.alpha.-dimethylbenzyl isocyanate, styrene, acrylonitrile, methacrylonitrile, sodium styrenesulfonate, and acrylamido-2-methylpropanesulfonic acid and the sodium salt thereof. PA1 acrylate esters, for example, methyl, ethyl, isopropyl, n-butyl, isobutyl, n-amyl, isoamyl, n-hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, cyclohexyl, phenyl, benzyl, 2-hydroxyethyl, and hydroxypropyl acrylates; PA1 methacrylate esters, for example, methyl, ethyl, isopropyl, n-butyl, isobutyl, n-amyl, isoamyl, n-hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, cyclohexyl, phenyl, benzyl, 2-hydroxyethyl, and hydroxypropyl methacrylates; PA1 the acrylates of other alkyl groups having 3-12 carbon atoms; PA1 the methacrylate of other alkyl groups having 3-12 carbon atoms; PA1 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, acrylonitrile, methacrylonitrile, glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether; PA1 unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, acrylic anhydride, methacrylic anhydride, maleic anhydride, itaconic anhydride, and fumaric anhydride; PA1 amino-containing monomers such as N-methylaminoethyl acrylate, N-methylaminoethyl methacrylate, dimethylaminoethyl acrylate, and dimethylaminoethyl methacrylate; PA1 aromatic vinyl compounds such as styrene, 2-methylstyrene, t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, and divinylbenzene; PA1 vinyl esters such as vinyl acetate, vinyl propionate, and fatty acid vinyl esters (e.g., "VeoVa", trade mark; product of Shell Japan Ltd.); PA1 halogenated vinyl compounds such as vinyl chloride; PA1 halogenated vinylidene compounds such as vinylidene chloride, and vinylidene fluoride; PA1 olefins such as ethylene, propylene, isoprene, butadiene and chloroprene; PA1 others such as vinylpyrrolidone, acrylonitrile, methacrylonitrile, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, neopentyl glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, trimethylol propane trimethacrylate, trimethylol propane triacrylate, tetramethylol methane triacrylate, tetramethylol methane tetraacrylate, allyl methacrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, isopropenyl-.alpha.,.alpha.-dimethylbenzyl isocyanate, and allyl mercaptan; and PA1 amides such as acrylamide, methacylamide, N-methylolmethacrylamide, N-methylolacrylamide, diacetoneacrylamide, and maleamide. PA1 (1) a process in which polymerization is conducted by adding a polymerization initiator in the presence of the ethylenically unsaturated monomer (a2); PA1 (2) a process in which a polymerization initiator is added and polymerization is then conducted while adding the ethylenically unsaturated monomer (a2) dropwise (suited when intense heat is given off by the polymerization); PA1 (3) a process in which a polymerization initiator is dissolved in the ethylenically unsaturated monomer (a2) and polymerization is conducted while adding the thus-prepared solution dropwise; and PA1 (4) a process in which a polymerization initiator is dissolved in an appropriate solvent and polymerization is conducted while adding the thus-prepared solution and the ethylenically unsaturated monomer (a2) dropwise at the same time but separately. PA1 (1) a process in which monomer(s) as component(s) for the protective colloid are mixed and then heated to a desired polymerization temperature, followed by the addition of a polymerization initiator to conduct polymerization; PA1 (2) a process in which a polymerization initiator is added and polymerization is then conducted while adding dropwise monomer(s) as component(s) for the protective colloid (suited when intense heat is given off by the polymerization); PA1 (3) a process in which a polymerization initiator is dissolved in monomer(s) as components (s) for the protective colloid and polymerization is conducted while adding the thus-prepared solution dropwise; and PA1 (4) a process in which a polymerization initiator is dissolved in an appropriate solvent and polymerization is conducted while adding the thus-prepared solution and monomer(s) as component(s) for the protective colloid dropwise at the same time but separately. PA1 (1) addition of the metal salt in a solid form to the aqueous emulsion; and PA1 (2) addition of the metal salt to the aqueous emulsion after converting the metal salt into an solution by dissolving it in a solvent capable of dissolving same at a predetermined concentration or higher. PA1 1. improvement in flexural strength; PA1 2. improvement in tensile strength; PA1 3. improvement in bonding strength (which leads to an improvement in the bonding strength to hardened mortar or concrete, plywood, metal, tiles or the like); PA1 4. retention of bonding strength after immersed in water; PA1 5. retention of bonding strength over a long period of time; PA1 6. reduction in the amount of water to be used and hence, an improvement in strength owing to the use of water in the reduced amount, because the redispersible polymer according to the present invention can improve the flowability upon mixing hydraulic cement and has effects as a water reducing agent; and PA1 7. prevention of introduction of air into a mixed cement because the mixing can be completed in a short time owing to the excellent redispersibility. PA1 8. improvement in anti-permeability. PA1 9. improvement in wear resistance.
Nevertheless, redispersible polymers produced by conventional techniques are accompanied by at least the following disadvantages because they use conventional spray drying:
A. Conventional Techniques for Polymer Particles
Conventional techniques for polymer particles will be described below. Polymer particles produced by such conventional techniques show either no redispersibility or dispersibility which is not fully satisfactory. Further, the below-described conventional techniques for the provision of polymer particles which show redispersibility all employ conventional spray drying and due to one or more drawbacks inherent to the conventional spray drying, they are unable to provide sufficient redispersibility.
Japanese Patent Laid-Open No. 193903/1984
Japanese Patent Laid-Open No. 193903/1984 in the name of TOSOH CORPORATION discloses a technique for readily obtaining an aggregate-free powder composition by polymerizing one or more unsaturated monomers in the presence of a special water-soluble copolymer which acts as a stabilizer or powdering agent across a particular pH value.
Described specifically, this technique is a production process in which, after a stable emulsion is polymerized in the presence of a water-soluble copolymer of methacrylamide and an unsaturated carboxylic acid, the resultant polymer is separated at pH 4 or lower, followed by dehydration and drying.
However, insofar as its disclosure is concerned, the process is understood to have the following inventive features.
In the invention disclosed in Japanese Patent Laid-Open No. 193903/1984, the water-soluble copolymer has the following two functions:
This technique makes it possible to obtain an aggregate-free powder by conducting emulsion polymerization in the presence of a water-soluble copolymer having a function as a stabilizer.
Namely, a radically-polymerizable, unsaturated-bond-containing monomer (e.g., styrene) (A) is first polymerized at pH 5 or higher in an aqueous medium in the presence of a water-soluble copolymer (B) of methacrylamide and an unsaturated carboxylic acid (preferably, methacrylic acid or itaconic acid), thereby obtaining an emulsion which is stable under the action of the component (B) as a stabilizer. The pH is then adjusted to 4 or lower to separate the resultant polymer from the emulsion under the action of the component (B) as a powdering agent. The thus-separated polymer is dehydrated and dried, whereby a powder composition is obtained.
Concerning the weight ratio of the radically-polymerizable, unsaturated-bond-containing monomer (A) to the water-soluble copolymer (B), it is preferred to use (B) in an amount of from 1 to 10 parts by weight per 100 parts by weight of (A). It is described that an amount of (B) smaller than 1 part by weight cannot exhibit sufficient powdering effect for the emulsion while an amount of (B) greater than 10 parts by weight leads to an increase in production cost and is hence not needed. As a matter of fact, (B) was used in an amount of 2 parts by weight per 100 parts by weight of (A) in Examples 7 to 9.
It is also disclosed that, when methacrylic acid or itaconic acid is used as an unsaturated carboxylic acid monomer upon production of a water-soluble copolymer, the resulting water-soluble copolymer has a function as a powdering agent at a composition ratio of methacrylic acid or itaconic acid to methacrylamide in a range of from 9/1 to 1/9. Further, as a method for lowering the pH, it is disclosed to add hydrochloric acid or the like under stirring.
The theme dealt with by the technique of this publication is limited to powdering of a polymer, so that redispersion of the polymer so powdered is not contemplated at all. The powdered polymers disclosed in this publication therefore has no inherent redispersibility.
Japanese Patent Publication No. 54973/1991
Japanese Patent Publication No. 54973/1991 in the name of Wacker-Chemie GMBH discloses a technique for producing dispersible powder having excellent flowability and good redispersibility by subjecting one or more ethylenically unsaturated compounds to emulsion polymerization in the presence of a specific protective colloid and a free-radical initiator and then drying the resultant polymer.
Described specifically, in an aqueous medium containing 5 wt. % or more of a protective colloid--which is selected from a water-soluble starch having an amylose content of 30 wt. % or less, a water-swellable starch, a dispersible starch, a cyanoalkylated, hydroxyalkylated or carboxylated starch or a water-soluble protein--and a free-radical initiator (e.g., isopropyl hydroperoxide), one or more copolymerizable, ethylenically unsaturated compounds are subjected to emulsion (co)polymerization, whereby an aqueous dispersion having a water content of from 10 to 75 wt. % is obtained.
This aqueous dispersion is next subjected to spray drying optionally after adding a detackifier (e.g., PVA) and/or an atomizing aid (e.g., dextrin) in an amount of 0 to 40 wt. % as needed.
Japanese Patent Laid-Open No. 210336/1991
Japanese Patent Laid-Open No. 210336/1991 in the name of Nippon Paint Co., Ltd. discloses a technique for obtaining crosslinked resin particles from a resin
Japanese Patent Publication No. 59324/1992
Japanese Patent Publication No. 59324/1992 in the name of BASF AG discloses a process for producing a polymer powder permitting storage at room temperature and having stick-free property and water redispersibility by spray drying an aqueous dispersion which contains a vinylpyrrolidone-vinyl acetate copolymer or a water-soluble alkali (or alkaline earth) metal salt of a naphthalenesulfonic acid-formaldehyde condensation product.
Described specifically, an aqueous dispersion of a polymer is spray-dried after adding, as a water-soluble polymer substance, a copolymer (A) obtained from 20-70 wt. % of vinylpyrrolidone and 30-80 wt. % of vinyl acetate and/or a water-soluble alkali metal salt or alkaline earth metal salt (B) of a naphthalene-sulfonic acid-formaldehyde condensation product in an amount of from 2 to 40 wt. % based on the polymer in the dispersion.
The redispersible polymer powder obtained in the above-described manner is suited as an additive especially for a hydraulic binder, for example, gypsum, cement, mortar and magnesia cement.
Japanese Patent Laid-Open No. 194681/1993
Japanese Patent Laid-Open No. 194681/1993 in the having a glass transition point of 0.degree. C. or lower by a particular post-emulsification method, which comprises subjecting the resin to the post-emulsification method after addition of specific plural substances to the resin, thereby obtaining crosslinked resin particles free from interparticulate cohesion and excellent in redispersibility and storage stability.
Described specifically, the technique is a process for obtaining crosslinked resin particles by post emulsification, which comprises the following steps: dispersing a resin component in water from a resin having a glass transition point (Tg) of 0.degree. C. or lower, for example, an elastomer such as acrylic rubber, polybutadiene, polyisoprene, chloroprene, poly (.epsilon.-caprolactone) or poly(tetramethylene glycol), forming an interior of each dispersed particle into a three-dimensional structure and then removing the aqueous medium. The process features that the resin component is subjected to the post emulsification after the resin component is added with a monomer (e.g., styrene) capable of affording a resin having a Tg 20.degree. C. higher in the polymerized form than the resin component and or a resin (e.g., PS) having a Tg 20.degree. C. higher than the resin component and also with a polyfunctional vinyl compound (e.g., neopentyl glycol methacrylate). name of Rohm & Haas Co. discloses a technique, which relates to a process for producing a novel redispersible core-shell polymer powder effective as a mortar modifier.
Namely, disclosed is a redispersible polymer powder obtained by spray-drying a core-shell polymer which has been produced by polymerizing cores in the presence of alkali-soluble shells and which is formed of cores and shells chemically grafted together owing to the use of a polyfunctional compound.
Described more specifically, disclosed is a redispersible polymer powder produced from a core-shell polymer which has shells made of an alkali-soluble emulsion polymer and cores made of a water-insoluble emulsion polymer, the polymer of each of said shells and the polymer of its corresponding core having been chemically graft-bonded together by the use of a polyfunctional compound. This core-shell polymer is produced by a two-step successive emulsion polymerization process, that is, by polymerizing cores of an alkali-insoluble emulsion polymer in the presence of an emulsion polymer which has been solubilized with an alkali. Use of the core-shell polymer powder of this invention as a cement modifier has been confirmed to improve physical properties of the powder and hence to provide cement mortar having improved properties.
Japanese Language Laid-Open Publication (PCT) No. 501575/1993
Japanese Language Laid-Open Publication (PCT) No. 501575/1993 in the name of Henkel KG Auf Aktien) discloses a process for the production of a stable polymer dispersion by employing as a stabilizer an amphoteric polymer which has excellent shear stability and water-proofness and is useful inter alia as a finish for textile products. The amphoteric polymer is obtained by adjusting the pH of an aqueous solution of a stabilizer composed of a starting amphoteric polymer to an isoelectric point with an acid or the like to cause the starting amphoteric polymer to precipitate from the aqueous solution, adjusting the pH of the aqueous solution to redissolve the precipitate, adding a catalyst and the like and then conducting emulsion polymerization.
Described specifically, the pH of an aqueous solution of a stabilizer composed of a starting amphoteric polymer is adjusted to an isoelectric point with a non-volatile acid or base to cause the starting amphoteric polymer to precipitate. Using a volatile base or acid, the pH of the solution is adjusted to a value desirable for emulsion polymerization, so that the precipitate is redissolved. Thereafter, an unsaturated monomer of the vinyl structure is neutralized with a non-volatile neutralizing agent and is added together with a catalyst and one or more optional aids, followed by emulsion polymerization so that the target dispersion is obtained.
B. Conventional Techniques on Protective Colloid Polymerization
Protective colloid polymerization is a polymerization process which is known to the public and is used publicly.
The concepts of the terms "protective colloid polymerization" and "protective colloid" as well as the concept and principle of protective colloid polymerization are disclosed in introductory textbooks, for example, Tsunetaka Matsumoto: "Kogyo Zairyo (Industrial Material), Emarushion Gairon (Introduction to Emulsion)", 24(3), 10-15.
In particular, visual and readily-understandable explanations are found in "FIG. 2 Shinsuisei Monoma no Nyuka Jyugo (Emulsion Polymerization of Hydrophilic Monomers" (page 12) and its description [under "Shinsuisei Monoma no Nyuka Jyugo (Emulsion Polymerization of Hydrophilic Monomers" on page 12] and further in "FIG. 3 Mizu Emarushion no Anteika (Stabilization of Aqueous Emulsion)" (page 13) and its description [under "Mizu Emarushion no Anteika (Stabilization of Aqueous Emulsion)" on pages 12-13].
Unless otherwise specifically indicated, all publications and parts thereof cited herein are incorporated herein by reference so that matters directly and conceivable by a person having ordinary knowledge in the present field of art based on the matters disclosed herein with reference to such cited parts shall be construed as being disclosed herein.
Illustrative of specific examples of known techniques on protective colloid polymerization are those disclosed in Japanese Patent Laid-Open Nos. 173003/1990 and 185607/1992, which will be described hereinafter.
Japanese Patent Laid-Open No. 185607/1992
Japanese Patent Laid-Open No. 185607/1992 in the name of Hoechst Gosei K. K. discloses an invention on a redispersible acrylic resin emulsion powder of the protective colloid type and its production process. Namely, an acrylic monomer is subjected to emulsion (co)polymerization in the presence of a specific amount of a chain transfer agent while using a water-soluble protective colloid. The resulting emulsion is spray-dried, whereby the above-described powder excellent in redispersibility, film properties and the like is obtained. Described specifically, using a water-soluble protective colloid (e.g., polyvinyl alcohol), an acrylic monomer (e.g., methyl methacrylate) is subjected to emulsion polymerization in the presence of a chain transfer agent (e.g., trichloroethylene) in an amount of from 0.1 to 50 wt. % on the basic of the acrylic monomer, optionally together with 30 wt. % or less of a copolymerizable monomer (e.g., styrene). The resulting acrylic resin emulsion is then spray-dried, so that a redispersible acrylic resin emulsion of the protective colloid type is obtained. The resin emulsion powder so obtained is suitably usable as an adhesive, a paint binder, a cement additive and the like.
Japanese Patent Laid-Open No. 173003/1990
Japanese Patent Laid-Open No. 173003/1990 in the name of Mitsui-Toatsu Chemicals Inc. discloses a technique for efficiently obtaining porous polymer particles without inclusion of impurities such as a dispersant, a diluent and the like by dispersing an oil phase, which contains a polymerizable monomer and a diluent, in an aqueous medium containing a dispersant and then polymerizing the resultant dispersion under specific conditions.
Described specifically, in an aqueous medium (b) containing 0.1-10 wt. % of a dispersant (a) which is a partially-saponified PVA having a saponification degree of 50-95%, an oil phase (e) containing a polymerizable monomer (c), which is a monomer insoluble or sparingly soluble in the component (b) and contains a vinyl group, and a diluent (d) which is soluble in the component (c) but insoluble or sparingly soluble in the component (b) and has no polymerizability is dispersed in the form of spheres of 1-50 .mu.m in diameter at a volume ratio of the component (b) to the component (c) in an range of from 10:1 to 1:1. While polymerizing the component (c), the dispersed particles are caused, in their spherical forms, to flocculate into sizes of from 0.1 to 3 mm in diameter so that a polymer particle flocculate is obtained. This flocculate is then washed to remove the component (a). Subsequent to extraction of the component (d), the flocculate is redispersed to sizes of from 1 to 5 .mu.m.
C. Technical Background Concerning Redispersibility and Film-Forming Properties
Redispersibility and Film-Forming Properties
Redispersible polymers or their powders include those incapable of forming films at room temperature when reconstituted to redispersions. To be usable for a wide range of applications, a redispersible polymer or a powder thereof whose reconstituted redispersion dries at room temperature into a film is however preferred. When an aqueous emulsion such as that capable of forming a film at room temperature is dried, a serious problem arises, that is, the polymer is so soft that dispersed particles of the polymer undergo aggregation and cohesion and the redispersibility is lost.
Anti-Binding Agent
To avoid mutual aggregation and cohesion of powder particles, it is known to add as an anti-binding agent a fine inorganic powder or a fine organic powder having no binding ability.
Such a method however involves a problem in that, when a film is formed by drying a redispersion, undesirous effects are given to various properties such as transparency. This has imposed a considerable limitation on the utility and application field.
Among applications of a redispersible polymer or its powder, a cement additive is expected to develop less problems even when fine inorganic power is mixed. Even in the case of such a cement additive, an increase in flow value is observed due to large hygroscopicity of the fine inorganic powder, thereby making it necessary to increase the water/cement ratio.
Further problems have also been observed, including production of cement products having high hygroscopicity and also production of cement products prone to dusting of fine powder and hence to non-uniformity in composition.
For such problems, it has been desired to develop a redispersible polymer which does not require such an anti-binding agent.
Core-Shell Polymers Having Alkali-Soluble Shells
Among the conventional techniques on redispersible polymer powders, the method making use of a core-shell polymer equipped with alkali-soluble shells is accompanied by a problem in redispersibility because the shells have a low density due to their solubility and are unable to completely prevent cohesion of particles during drying.
Moreover, omission of an anti-binding agent results in a new problem that the cohesion of particles cannot be prevented.
Spray Drying Technique
Most redispersible polymer powders are produced by spray drying, which directly obtains powder by causing water to evaporate while preventing aggregation.
Conventional spray drying however involves a problem in redispersibility, because powder is dried usually at a temperature as high as 100.degree. C. or higher and cohesion of particles cannot be prevented completely.
In some instances, a deposit or the like occurs on an inner wall of a drying tower upon spray drying, leading to a substantial reduction in yield.
A further serious problem is also involved in that enormous time and energy are needed in large-scale production or batchwise production.
The present inventors considered that the conventional techniques for the production of a redispersible polymer or its powder are not satisfactory for the need for such enormous time and energy.
D. Technical Background Concerning Cement Additives
Dai 50 Kai Semento Gijyutsu Taikai Koen Yoshishu (Abstracts of Lectures at the 50th Cement Technology Symposium), 324-325, 1996
A polymer cement mortar with a redispersible powder resin mixed therein is described to still involve an unsolved technical problem in redispersibility or the like and to result in lowered compression strength and/or flexural strength in some instances.
Dai 50 Kai Semento Gijyutsu Taikai Koen Yoshishu (Abstracts of Lectures at the 50th Cement Technology Symposium), 322-323, 1996
A polymer cement mortar with a redispersible powder resin mixed therein is described to have tendency to permit introduction of air into cement so that in some instances, the compression strength and/or flexural strength may be reduced to adversely affect various physical properties.
In view of the above-described teachings, development of a redispersible powder resin excellent in redispersibility, if succeeded, is expected to provide polymer cement mortar with improved physical properties because such a redispersible powder resin makes it possible to complete the mixing of water, cement, sand and the like in a short time and hence to reduce the amount of air to be introduced into cement.